Since the assumptions on which the flexure formula are based do not hold true at high stresses approaching failure, modulus of rupture is a fictitious value; however, it is convenient for purposes of evaluation and is commonly used. The modulus of rupture ranges from 11 to 23 percent of the compressive strength. The use of rough-textured or angular aggregates results in relatively high flexural strength as compared to compressive strength.

An approximate relationship between flexural and compressive strength is